1. Field of the Invention
The invention relates to a closing device for large passages, cavities or chambers in a prestressed pressure vessel. More particularly, the closing device safely seals areas housing components of nuclear power plants. The basic element of the device is a cover, narrowing entirely or partially in the upward direction and resting on the edge of the passage, cavity or chamber.
2. Background of the Prior Art
Certain components of nuclear power plants, such as for example heat exchangers, must be readily accessible for purposes of repair or replacement and are, therefore, housed within a prestressed pressure vessel in large passages. These passages must be adequately sealed and shielded during the normal operation of the reactor. Usually, closing devices of concrete, steel or cast iron are used for the purpose. These closing devices must withstand the high internal pressures in the vessel. The pressure vessel itself usually consists of a prestressed structure of concrete, steel or cast iron.
A closing device of this type is known, for example, from West German Offenlegungsschrift 27 10 859. It consists of a pressure-bearing, reinforced concrete body held by vertical prestressing members of the pressure vessel and an elastic sealing cover made of steel. By means of the vertical prestressing elements which may pass through the pressure-bearing, reinforced concrete body itself, the reinforced concrete body is pressured onto the sealing cover and the cover, with its flange, onto the liner arranged in the passage.
In West German Offenlegungsschrift No. 17 84 369, a closing device for a manhole opening in the wall of a reinforced concrete pressure vessel is disclosed. The reinforced concrete part comprises an annular outer part and an inner part. Both parts have circumferential prestressing and the annular outer part additionally is provided with channels to receive vertical prestressing elements which are also passed through the reinforced concrete pressure vessel. A projection protrudes from the outer circumference, which cooperates with a correspondingly shaped projection on the outer part. To remove the closing device, both parts must be dismantled, i.e. it is necessary to release the prestressing elements passing through the pressure vessel and the outer part.
Another arrangement for sealing an opening in a pressure vessel is shown in West German Offenlegungsschrift No. 16 84 926. It comprises a cover consisting of reinforced concrete with a conical outer boundary surface and a plurality of wedge-like abutments, whereby the cover is supported on the mantle of the pressure vessel. The closing device in this instance is not set on the opening in the vessel, but is inserted from above in the opening. The cover is designed in several pieces and clamped together by clamping elements from several sectors.
In West German Offenlegungsschrift No. 22 34 491 again a closing device for a passage in a pressure vessel is described. The closing device consists of concrete and is inserted from above into the passage. Prestressing is induced in the closing device by means of compressive stress acting upon its circumference. In order to secure the closing device against axial forces and to transfer such forces, a primary retaining device is provided, whereby the closing device is supported on a flange of the passage liner.
The retaining device consists of a plurality of segments, designed to form together a truncated cone-shaped annulus. By means of a secondary retaining device, the closing device is to be secured in case of a failure of the primary retaining device. The secondary retaining device comprises a series of elements fastened in part to the circumference of the closing device and in part to the passage liner and brought into engagement with each other. They may be released at least in part from each other in order to render possible the removal of the closing device.
The present invention is based on this state of the art, wherein it has as its object to provide a closing device for large passages of the above-described design type. The closing device of this invention is to be characterized by a high degree of safety, economical manufacture and handling and ready dismantling of the cover.